The present invention relates to an improved method for the treatment and disinfection of seafood, and more particularly, but not by way of limitation, to a method for disinfecting seafood by acidification of an aqueous solution of a chlorine dioxide liberating compound, such as a metal chlorite.
Chlorine has been known to be an effective bactericide since the early 1940s. The concentration of chlorine that may be utilized as a disinfectant is limited, however, due to environmental and health concerns relating to the transfer of chlorine into the air. Therefore, low concentrations such as 20 ppm are typically employed for disinfection. Such a low concentrations, however, dilute the biocidal effects of the chlorine. Moreover, aqueous chlorine, which has been used for the sanitation of meats and seafood, creates safety concerns because of the formation of trihalomethanes and other potentially harmful reaction products.
As an alternative to chlorine, chlorine dioxide (ClO2) has been explored as a potential substitute as a biocide. Chlorine dioxide is a strong oxidant and may be applied in a variety of processes including cellulose bleaching and treatment of waste water and drinking water. Moreover, chlorine dioxide has been effective as a potent bactericidal agent, significantly reducing the bacterial populations in poultry and meat. E.g., see U.S. Pat. No. 5,389,390 issued to Kross. Moreover, chlorine dioxide has long been used in the treatment of water supplies. Chlorine dioxide is also superior to gaseous chlorine in the removal of odors and tastes, and in destroying and removing algae or other organic material. Chlorine dioxide is further advantageous in that its biocidal activity is not affected by high pH or the presence of nitrogenous compounds. In essence, chlorine dioxide retains its biocidal capacity to a significantly greater extent and over a wider pH range than does gaseous chlorine. Since minimal reaction products, including trihalomethanes are produced in treated water, chlorine dioxide is an effective and safe substitute for aqueous chlorine.
However, certain problems have been encountered in the use of chlorine dioxide as a biocide. Chlorine dioxide as a concentrated gas is explosive and poisonous. Accordingly, chlorine dioxide is not often shipped in the gaseous state. It has thus become common practice to employ a chlorine dioxide releasing compound such as a sodium chlorite powder for safety reasons. Generation of chlorine dioxide from sodium chlorite or other chlorine dioxide releasing compounds is usually effected by addition of an acid, bleach (hypochlorite), or chlorine to the chlorine dioxide releasing compound.
Prior art techniques for disinfecting food substances such as those disclosed in U.S. Pat. No. 5,389,390 issued to Kross and U.S. Pat. No. 5,185,161 issued to Davidson et al. disclose acidifying and relatively dilute solutions of a metal chlorite for the purpose of disinfection. However, because these techniques acidify dilute solutions, they are often unable to effectively kill particularly troublesome bacteria such as Listeria Monocytogenes. Furthermore, the low pH of the solutions applied to the food product often has a deleterious effect on the product.
Fresh seafood products are particularly susceptible to spoilage by naturally occurring bacterial micro-flora. Additionally seafood products may carry disease-causing organisms such as Listeria Monocytogenes and Escherichia Coli and other enteric organisms which can cause serious health problems and in some cases death. Thus, there continues to be a need for a method for disinfecting seafood products.
The present invention provides a method for the disinfection of seafood. The inventive method includes the steps of (a) preparing a concentrated aqueous solution of a chlorine dioxide liberating compound having a concentration of from about 0.2% to about 25% by weight of the chlorine dioxide liberating compound and having an amount of an acid sufficient to adjust the pH to from about 1.0 to about 5.0; (b) diluting the concentrated aqueous solution to provide a dilute, acidified solution having a concentration of from about 0.00017% to about 0.17% by weight of the chlorine dioxide liberating compound; and (c) contacting the dilute, acidified solution with seafood to disinfect the seafood. Preferably, the chlorine dioxide liberating compound is an alkali metal chlorites, with sodium chlorite and potassium chlorite being particularly preferred. The acid may be any acid generally regarded as safe, as that term is used in the Code of Federal Register, 21 CFR 170.35 and 21 CFR 170.30.
The present invention provides a process for removal of bacteria and control of naturally occurring spoilage organisms on seafood, including without limitation, finfish, shellfish, and crustaceans. The present invention increases shelf-life and product freshness.
In accordance with the present invention, an aqueous solution is prepared containing from about 0.2% to about 25% by weight of a chlorine dioxide liberating compound, preferably a metal chlorite, and containing an acid in an amount sufficient to adjust the pH of the solution to from about 1.0 to about 5.0. The acid used may be any acid which is xe2x80x9cgenerally regarded as safexe2x80x9d (i.e., a xe2x80x9cGRASxe2x80x9d acid as that term is used in the Code of Federal Register, 21 CFR 170.35 and 21 CFR 170.30). After acidification, the aqueous metal chlorite solution is then diluted with water to a use concentration of about 0.00017% to about 0.17% by weight of the chlorine dioxide liberating compound, which corresponds to a concentration of about 0.0001% to about 0.1% by weight of total available chlorine dioxide. Total available chlorine dioxide is the sum of the dissolved chlorine dioxide gas and chlorite ion concentrations. The diluted, acidified chlorite solution will generate from about 0.01 to 50 ppm chlorine dioxide and will have a pH in the range of from about 5.0 to about 8.0.
Incubation time can vary from 1 minute to 1 hour, depending upon the concentration of the aqueous solution. The higher the concentration of the chlorine dioxide liberating compound, the less time required for incubation. For a solution having 3.35 by weight of sodium chlorite at a pH of 2.5, the preferred incubation time will be about 10 minutes.
The initial acidification of the relatively concentrated aqueous solution of the chlorine dioxide liberating compound provides a somewhat rapid generation of chlorine dioxide. The dilution step essentially quenches the reaction process and raises the pH of the solution, allowing further generation of chlorine dioxide to occur over a more extended period of time. When this solution is applied to seafood products, it provides certain advantages over prior art methods. First, the acidification of the relatively concentrated solution generates sufficient chlorine dioxide to serve as a xe2x80x9cshockxe2x80x9d treatment to kill particularly troublesome bacteria and other microbes that would be unresponsive to other approaches. Second, the pH of the solution is in the range of from about 5.0 to about 8.0 when it is applied to the seafood products. The more neutral pH solution that is applied is far less harmful to the seafood product than prior art approaches. Third, the quenching of the reaction process by dilution allows the solution to generate chlorine dioxide over a more extended period of time than approaches which merely acidify concentrated solutions of a metal chlorite and then directly apply the acidified chlorite solution to the item to be disinfected.
In a particularly preferred embodiment, an aqueous sodium chlorite solution having a concentration from about 0.5% to about 4% is prepared. A strong inorganic acid, such as phosphoric, hydrochloric or sulfuric, or an organic acid such as citric acid is added to the solution in sufficient amount to adjust the pH from about 2.5 to about 2.9. The solution is then diluted to a use concentration of from about 0.0005% to about 0.01% total available chlorine dioxide by weight, as defined above.
Preferred acids are strong inorganic acids such as phosphoric, hydrochloric or sulfuric acid, as well as organic acids such as citric. Preferred metal chlorites are alkali chlorites such as sodium or potassium chlorite. The metal chlorite is present for the liberation of chlorine dioxide. Because chlorine dioxide gas is highly unstable, it is generated in solution. While any chlorine dioxide liberating compound may be used, water-soluble chlorites are preferred because they are readily available and inexpensive.
The acidified sodium chlorite solution containing chlorine dioxide may be contacted with seafood products directly or by addition to process waters which contact the seafood products during normal processing operations both on board ships and at onshore seafood processing and point of sale facilities. In the event that the acidified chlorite solution of the present invention is added to processing water, the addition is to be taken as the final dilution step described above so that the concentration of the chlorite in the processing water is within the desired use concentration range stated above.
Acidified metal alkali chlorite solutions contain chlorine dioxide as the active ingredient and the biocidal component which, when in contact with the seafood product, provides the desired technical effect of inhibiting the growth of naturally occurring spoilage bacteria, thereby resulting in reduced spoilage of seafood, enhanced freshness and more aesthetically pleasing seafood, with resultant extension of the storage life for the treated seafood. Seafood products which may be treated in accordance with the present invention include, but are not limited to, fish, including freshwater fish, scallops, shrimp, crabs, clams, oysters and squid.
The acidified chlorite solution containing chlorine dioxide may be treated as a batch process or fed by suitable controlled metering devices into water such as brine water soak solutions, potable fresh processing waters and seawater process waters. The process waters, thus described, are intended for use in the cooling, cleaning, washing and soaking of seafood as may be performed in accordance with Good Manufacturing Practices for seafood processing operations. Appearance and quality are not compromised when acidified sodium chlorite solutions containing chlorine dioxide are utilized in the concentrations cited in this patent application.